1. Field of the Invention
The present invention relates to a method of fabricating an insulating resin material that is useful as a material for members requiring insulation and heat dissipation.
2. Description of Related Art
Since resins formed of macromolecular compounds are low-cost insulating materials with high moldability, they are used in various electric components as substrates for electronic circuit boards, insulating materials for motors, insulating adhesives, or the like. Recently, such electronic components have been configured with highly dense constructions and realized high output, resulting in increased heat generation from those electronic components. Accordingly, measures to dissipate heat of the electric components are strongly desired.
To solve such a problem, related arts employ a method that the interior of the resin is filled with a filler formed of an inorganic material such as alumina or silica, thus enhancing heat conductivity of the resin. For example, Japanese Patent Application Publication No. H11-233694 discloses a technology such that particles of an inorganic material such as crystalline silica or aluminum oxide are added into a macromolecular resin to provide heat conductivity. In such a case, a continuum formed with inorganic filler particles joined together functions as a heat conducting pathway. In other words, the inorganic filler particles filled in the resin must be in contact with each other. Accordingly, it is required that a large amount of inorganic filler be filled in the resin to achieve efficient heat conduction.
In consideration of such a problem, for example, Japanese Patent Application Publication 2010-189600 discloses a method of fabricating an insulating resin material, by which core/shell particles including core particles having a macromolecular compound and shell layers coating the core particles and having a heat-conductive and insulating inorganic compound are fabricated by seed diffusion polymerization in an ionic liquid, and by which the insulating resin material is molded from an aggregate of the core/shell particles.
Further as another embodiment, Japanese Patent Application Publication 2010-144153 discloses a method of fabricating a insulating resin material by which an aggregate of core/shell particles in which a core formed of a macromolecular compound is coated with a shell layer formed of an inorganic compound, is compression-molded into a compact, the molded compact is impregnated with a sol, the sol is next gelatinized, and the gel is then hardened to obtain the insulating resin material.
According to these embodiments, use of the core/shell particles enables reduction in the ratio of inorganic compound which serves as the shell layer to the macromolecular compound which serves as the core and enables obtainment of an insulating resin material with high heat dissipation.
As described above, in molding an insulating resin material from an aggregate of core/shell particles, compression-molding is preferable. However, control of temperature, pressure, and time is required to continuously form shell layers of an insulating resin material without interposing gaps among the particles in the aggregate. An investigation for finding out the optimum conditions requires a large amount of time. Even if the optimum conditions were found, limited shapes of the insulating resin material might be available.
In other words, differently from insulating resin materials formed of only a macromolecular compound, the shell layers of insulating resin materials formed of core/shell particles are inorganic layers. Accordingly, since the shells are not softened by pressure, the insulating resin materials tend to have narrow adequate conditions for molding compared to the compacts formed of only a macromolecular compound.
Further, differently from the insulating resin materials formed of only a macromolecular compound, molding of the insulating resin materials from an aggregate of core/shell particles requires a large amount of energy for heating and pressurization, resulting in a higher fabrication cost.